This invention relates to development system for electrostatic processsors and, more particularly, to split housings for magnetic brush development systems.
In a conventional electrostatic printing process of the type described in Carlson's U.S. Pat. No. 2,297,691 on "Electrophotography", a uniformly charged photoreceptor is selectively discharged in an image configuration to provide a latent electrostatic image which is then developed through the application of a finely divided, resinous material, called "toner". As is known, that process has enjoyed outstanding commercial success, especially in plain paper copiers and duplicators. Nevertheless, substantial effort and expense are still being devoted to the perfection of the process, including the development step.
The vehicle normally used in electrostatic processors to deliver the toner is a multi-component developer comprising toner particles and relatively coarse "carrier" particles. The toner and carrier (or sometimes carrier coating) are formed from materials which are removed from each other in the triboelectric series, thereby enabling a triboelectric charging process to be employed to induce electrical charges of opposite polarities on the toner and carrier particles. The polarity of the charge for the toner particles is selected to oppose the charge of the latent image so that there are competing electrostatic forces acting on those particles. Specifically, the toner particles at least initially tend to be attracted to the carrier particles, but are subject to being electrostatically stripped therefrom whenever the developer is brought into the immediate proximity of or actual contact with an image bearing photoconductor.
A marked improvement in the development process, and especially the solid area coverage that can be obtained, has recently been realized with the advent of so-called "magnetic brush" development systems. As is known, those systems are conventionally supplied with a developer containing a ferromagnetic carrier so that a shaped magnetic field and one or more rotatably driven applicator or development rolls may be used to control the flow of developer through the development zone. Moreover, there often also are one or more rotatably driven transport rolls which participate with the shaped field in controlling the flow of developer between the sump and the development zone.
Experience with magnetic brush development systems has shown that the spacing between the photoreceptor and the development rolls and between the development rolls themselves, as well as any transport rolls, is critical. Not only is the effectivity of the magnetic field directly dependent on the photoreceptor-to-development roll spacing and roll-to-roll spacing, but the usual practice is to electrically bias the development roll or rolls to create an electrical field tending to suppress background development. That, of course, further increases the sensitivity of the system to any change in the photoreceptor-to-development roll spacing.
One of the problems that has been encountered in applying magnetic brush development systems to drum-type processors is that the drum has circumferentially distributed radial run-out variations which tend to vary the photoreceptor-to-development roll spacing.